Our long term objective is to advance our understanding of the role of micro RNAs (miRNAs) in hepatocarcinogenesis. miRNAs are highly conserved -19-25 nucleotides noncoding RNAs some of expressed in plants and animals, are primarily involved in gene silencing. In animals, miRNAs function either by imperfect complimentary base pairing at multiple non-overlapping sites on 3'-UTRs of target genes or by mediating degradation of target mRNAs. The biological function of only a few miRNAs is known. Recent studies have shown that the expression of the miRNAs are differentially regulated in human cancers of different origins and the targets of some of the miRNAs act as oncogenes or tumor suppressor genes. Many miRNAs are expressed in a tissue-specific manner that is markedly altered in human cancers. The objective of this project is to elucidate the role of a liver specific micro RNA (mir-122a) in hepatocarcinogenesis. Hepatocellular carcinoma is the fifth most prevalent cancer in the world and is the third leading cause of cancer related death. Using miRNA microarray analysis we observed differential regulation of some miRNAs during the multistage hepatocarcinogenesis process induced in folate/methyl-deficient rats. Among these the expression of mir-122a, an abundant liver specific miRNA, was significantly down regulated in all tumors. Extension of this study to human primary hepatocellular carcinomas showed dramatic decrease in mir-122 expression in tumors. In the present study we will explore the role of mir-122a in hepatocyte differentiation and hepatocarcinogenesis. The specific aims of the present proposal are to: 1) measure expression of mir- 122a by real time RT-PCR or northern blot analysis in a large number of human HCCs to determine whether its down regulation is characteristic of HCC of specific etiology; 2) determine whether mir-122a is involved in hepatocyte differentiation in mouse ES cells or rat hepatocytes by antisense oligo and 3) investigate whether its overexpression in nonexpressing human hepatocellular carcinoma cell lines inhibits growth in culture and anchorage independent growth or promotes apoptosis. It is hoped that this study could establish mir-122a as a biomarker for hepatocellular carcinomas that can provide novel molecular target for liver cancer therapy. Further, this proposal fits well with the mission/goals set forth by multiple institutes that include NCI, NIDDK and NIAAA n the etiology, prevention and treatment of hepatocellular carcinomas. [unreadable] [unreadable] [unreadable]